We have already made much ado over play streets, a brilliantly simple way to address the lack of outdoor play opportunities in cramped urban areas. By petitioning a city to close a residential street to cars at a regularly scheduled time, a community gets an "instant playground," even if it lacks swings and monkey bars.
Perhaps the most inspiring play street is in the Jackson Heights neighborhood in Queens, N.Y. Here's a brief overview from StreetFilms.org:
Back in 2008, Jackson Heights residents banded together to win car-free Sundays on 78th Street, creating a new, temporary public space for children and families in one of NYC’s most park-starved neighborhoods. This year neighborhood activists aimed much higher: They wanted to make the street car-free 24-7 for the entire months of July and August.
It's hard to understand the true power of a play street until you see it in action:
Photo courtesy of Transportation Alternatives.